Performance customization system and process for optimizing xDSL performance

ABSTRACT

A system and process for customizing the performance of an xDSL communication system in which a transmitting modem and/or a receiving modem will negotiate a performance parameter for adjustment.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. utility application entitled,“PERFORMANCE CUSTOMIZATION SYSTEM AND PROCESS FOR OPTIMIZING xDSLPERFORMANCE,” having Ser. No. 09/102,176, filed Jun. 22, 1998, nowissued as U.S. Pat. No. 6,647,058, which is entirely incorporated hereinby reference. Furthermore, this application claims the benefit of U.S.Provisional Application No. 60/050,564, entitled “Power Adaptive xDSL,”filed Jun. 23, 1997, which is entirely incorporated herein by reference.

BACKGROUND

With the explosion in the growth of Internet usage among both businessesand households, telephone companies have been pressured to provideaffordable, high bandwidth access that will support high-speedmultimedia services, such as video on demand, high speed Internetaccess, and video conferencing. To meet this demand, telephone companiesare increasingly turning to DSL technology. DSL, while having severaldifferent embodiments, can provide throughput rates over 400 timesfaster than that available through traditional 14.4 kbps modems. Forexample, the following manifestations of DSL technology are eitheravailable today or are currently being tested on a trial basis:Asymmetric Digital Subscriber Line (ADSL), which has a throughput of 32kbps to 8.192 Mbps downstream to the customer and 32 kbps to 1.088 Mbpsupstream to the network; Rate Adaptive Asymmetric Digital SubscriberLine (RADSL), which is a rate adaptive variation of ADSL; High-bit-rateDigital Subscriber Line (HDSL), which offers full duplex throughput atT1 (1.544 Mbps) or E1 (2.048 Mbps) data rates; Symmetric DigitalSubscriber Line (SDSL), which provides bi-directional throughput at datarates ranging from 160 Kbps-2.084 Mbps; and Very high-bit-rate DigitalSubscriber Line (VDSL), which provides high data rates for customersclose to the central office (e.g., 51 Mbps for subscribers within 1000feet). But most importantly, xDSL offers these high data rates over astandard copper telephone line. Thus, with such a large, embedded coppernetwork already in place, network operators view xDSL technology as ameans for extending the life of their investment in copper by manyyears.

Inasmuch as xDSL is deployed over the copper network, it is susceptibleto the same unwanted noise signals that plague traditional copper basedcommunication systems. Noise can be generated by components bothinternal to the communication system, such as resistors and solid statedevices, and sources external to the communication system, such asatmospheric noise, high-voltage power lines and electric motors.

It is well known from information theory that the capacity of a channel(i.e., maximum data rate) is directly related to the logarithm of theratio of the signal power to the noise power on the channel. Therefore,to support the high data rates associated with xDSL, it would seemdesirable to boost transmission power levels to boost thesignal-to-noise ratio. As discussed in the foregoing, however, most xDSLsystems operate across a broad range of data rates. Thus, if thetransmission power level is statically set to support the highest ratepossible, this will result in a waste of power for data sessions runningat lower throughputs. Moreover, high transmission power levelsunfortunately contribute to a phenomenon known as crosstalk, which isperhaps the most common and troubling source of noise in a network.

Crosstalk is defined as the cross coupling of electromagnetic energybetween adjacent copper loops in the same cable bundle or binder.Crosstalk can be categorized in one of two forms: Near end crosstalk,commonly referred to as NEXT, is the most significant because the highenergy signal from an adjacent system can induce relatively significantcrosstalk into the primary signal. The other form is far end crosstalkor FEXT. FEXT is typically less of an issue because the far endinterfering signal is attenuated as it traverses the loop. Crosstalk isa dominant factor in the performance of many systems. As a result, xDSLsystem performance is often stated relative to “in the presence of othersystems” that may introduce crosstalk. Therefore, in central office (CO)environments where many xDSL loops or other circuits are bundledtogether in the same cable binder, it is often desirable to minimizetransmit power levels to the lowest levels possible that will stillsupport the desired data rates to reduce the effects of crosstalkbetween the loops.

Alternatively, where maximum throughput is sought, it becomes desirableto maintain the transmit power level of a given xDSL communicationsession thereby allowing the data rate to be maximized within thelimitations imposed by the noise characteristics of the channel.Optimization of xDSL performance in a central office environment wouldtypically require a combination of both power reduction on some channelsand increased throughput or data rates on other channels.

In addition to crosstalk, there may be other reasons to adapt powerlevels. One of these is to reduce unwanted noise created by the systemitself. Certain impairments on the copper loop, such as bridged taps (anunterminated parallel length of wire) may create reflections anddistortion energy that can reduce the overall performance of the system.Reducing the power in a frequency band that creates distortion energy orincreasing the power in a band that does not create distortion energycan improve the performance of the overall system.

In view of the foregoing discussion, what is sought is an xDSL systemand process that dynamically adjust the transmit power levels, datarates, and other defined performance parameters of one or more specificcommunication sessions to customize overall system performance.

SUMMARY OF THE INVENTION

Certain advantages and novel features of the invention will be set forthin the description that follows and will become apparent to thoseskilled in the art upon examination of the following or may be learnedwith the practice of the invention.

One embodiment is generally directed to a performance customizationsystem and process for optimizing xDSL performance. Broadly stated, animproved receiving modem according to one embodiment includesnegotiating means that the receiving modem uses to negotiate with atransmitting modem to select a particular xDSL performance parameter tobe optimized. In another embodiment, the receiving modem may includemeans that are used to calculate the signal-to-noise ratio on the xDSL.Finally, the receiving modem includes means capable of requesting anadjustment in the selected performance parameter.

According to another embodiment, an improved transmitting modem isdisclosed that includes negotiating means used to negotiate with areceiving modem to select an xDSL performance parameter to be optimized.The transmitting modem further includes means responsive to performanceparameter adjustment requests that are sent from a receiving modem.Further means are included in the transmitting modem for making therequested adjustment to the xDSL performance parameter.

An embodiment can also be viewed as providing a method for customizingthe performance characteristics of an xDSL receiving modem. In thisregard, the method can be broadly summarized by the following steps: Thereceiving modem negotiates with a transmitting modem to select an xDSLperformance parameter for optimization. A signal-to-noise ratio iscalculated and, based on this result, an adjustment request is made forthe selected xDSL performance parameter.

Similarly, an embodiment provides a method for customizing theperformance characteristics of an xDSL transmitting modem. The methodcan be broadly summarized as follows: The transmitting modem negotiateswith a receiving modem to select an xDSL performance parameter foroptimization. An adjustment request for the selected xDSL performanceparameter is received and, based on this request, the performanceparameter is adjusted.

According to an embodiment, the modems will choose either the data rateor the transmission power level as the performance parameter foradjustment. The non-selected performance parameter is assigned a fixedvalue while the selected performance parameter will undergo adjustmentuntil the system operates at a data rate that is marginally supported bythe transmission power level.

In a multiple xDSL system in which the xDSLs affect each others'performance through crosstalk, another embodiment allows a first modempair to instigate a transmission power reduction, which will in turnallow a second modem pair to either increase its present data rate ordecrease its transmission power. Through this combination oftransmission power adaptation and data rate adaptation, it is possibleto reduce the performance variance between the individual communicationsessions or customize the performance profile according to specificcustomer requirements.

Additional advantages will become apparent from a consideration of thefollowing description and drawings:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other features of the present invention will be more readily understoodfrom the following detailed description of specific embodiments thereofwhen read in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a prior art xDSL communication system;

FIG. 2 is a detailed block diagram of the xDSL performance customizationsystem;

FIG. 3 is a transmit power level optimization flow chart for the xDSLperformance customization system of FIG. 2;

FIG. 4 is a data rate optimization flow chart for the xDSL performancecustomization system of FIG. 2; and

FIG. 5 is a block diagram illustrating the application of the xDSLperformance customization system in an environment where multiple xDSLloops are bundled together.

DETAILED DESCRIPTION

While the invention is susceptible to various modifications andalternative forms, a specific embodiment thereof is shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit variousembodiments of the invention to the particular form disclosed, but onthe contrary, embodiments of the invention cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the claims.

A general model for a prior art xDSL communication system 8 isillustrated in the block diagram of FIG. 1. The system comprises atransmitting modem 11 and a receiving modem 13 that communicate with oneanother over an xDSL 16. Transmitting modem 11, through the use of amodulator, uses a message signal, generally known as a modulating orbaseband signal, to modulate a carrier signal to produce what iscommonly referred to as a modulated signal. As in any data transmissionevent, however, the signal received by a demodulator at receiving modem13 will consist of the modulated signal, modified by distortions imposedby the transmission system, plus noise that is inserted betweentransmission and reception.

Noise can be divided into four categories: thermal noise,intermodulation noise, crosstalk and impulse noise. Thermal noise is dueto thermal agitation of electrons in a conductor and is a function oftemperature. This type of noise is present in all electronic devices andtransmission media and is usually referred to as white noise, inasmuchas it is uniformly distributed across the frequency spectrum. A secondtype of noise, known as intermodulation noise, occurs when signals atdifferent transmission frequencies share the same transmission medium.The effect of intermodulation noise is to produce signals at a frequencythat is the sum or difference of two original frequencies. Crosstalk,which was discussed hereinbefore, can be broadly described as theunwanted coupling of signals between signal paths. The last type ofnoise, impulse noise, is the most unpredictable. Impulse noise consistsof irregular pulses or noise spikes of short duration that are typicallygenerated from external electromagnetic sources such as lightning,electric machinery and/or faults and flaws in the communication system.

Measures can be taken to counteract or at least minimize the effects ofintermodulation and crosstalk noise, but thermal and impulse noise areever present in virtually any electronic, copper based communicationsystem. Therefore, for demodulator 20 to demodulate the modulated signalto obtain the original message signal, the ratio of the modulated signalpower to the noise signal power must exceed a certain level. Typically,this ratio is referred to as the signal-to-noise (S/N) ratio and isreported in decibels according to EQ. 1 as follows:(S/N)dB=10 log(signal power/noise power)  EQ. 1

Moreover, the maximum rate at which data can be transmitted across xDSL16 is directly related to the logarithm of the ratio of the signal powerto the noise power on the channel as expressed in EQ. 2 where the datarate is expressed in bits per second and W represents the bandwidth ofthe channel in hertz as follows:data ratebps=W log 2(1+(signal power/noise power))  EQ. 2

Nevertheless, simply boosting the transmit power level at transmittingmodem 11 to its maximum value to support the high data rates of an xDSLcommunication session may result in unnecessary power consumption fordata sessions running at lower throughputs as discussed hereinbefore.Various embodiments of the present invention overcomes this problemthrough dynamic adaptation of the transmission power level.

With reference now to FIGS. 2 and 3, transmission power adaptationperformed by various embodiments will be discussed. The communicationsystem 10 of FIG. 2, comprising transmitting modem 12 and receivingmodem 14, is used for simplicity. The principles discussed herein canreadily be extended to a duplex environment. According to the xDSLcommunication system 10 depicted in FIG. 2, transmitting modem 12comprises a central processing unit (CPU) 22 in communication withmodulator 18, communication port 24 and memory 26. Memory 26 holdssoftware control program 27 and database 29. Similarly, receiving modem14 comprises CPU 28 in communication with demodulator 20 and memory 30.Memory 30, likewise holds software control program 31 and database 33.Demodulator 20 also comprises power measurement component 32. Controlprograms 27 and 31, in conjunction with databases 29 and 33, areexecuted by CPUs 22 and 28 and provide the control logic for theprocesses to be discussed herein.

FIG. 3 provides a flow chart for an embodiment performing transmit poweradaptation. The process begins with step 34 in which a maximum data rateis negotiated between transmitting modem 12 and receiving modem 14. Thisnegotiation can be carried out in a variety of embodiments. For example,receiving modem 14 could maintain a table of possible data rates indatabase 33, one of which is retrieved by control program 31 and thentransmitted to transmitting modem 12 as part of an initializationprocedure. Similarly, control program 27 in transmitting modem 12 couldselect a data rate from a table stored in database 29 for transmissionto receiving modem 14 as part of an initialization procedure. Regardlessof which modem initiates the establishment of the maximum data rate, thetwo modems can exchange messages according to any desired protocol untila mutually agreed upon rate is arrived at.

Once a maximum data rate has been established, receiving modem 14 willdetermine the net S/N ratio. Again, this determination can be made usinga variety of well known techniques. One common technique is fortransmitting modem 12 to cease transmission for a specified period.During this silent period, power measurement component 32 reads thenoise present on xDSL 16 and calculates the power spectral density (PSD)of the noise. Following the silent period, transmitting modem 12transmits a test pattern of data at a default power level allowing powermeasurement component 32 to calculate the PSD of the modulated signalplus noise. The previously calculated noise component can then besubtracted from the combined noise plus signal measurement to computethe net S/N ratio.

In step 38, receiving modem 14 determines whether the previouslycalculated S/N ratio will support the data rate originally arrived at instep 34. In one embodiment, this process will involve control program 31indexing a table stored in database 33 in which minimum S/N ratios arecorrelated with a list of possible data transmission rates andretrieving the minimum S/N ratio required for the current data rate.This table can be constructed using EQ. 2, which was set forthpreviously. It should be noted, however, that EQ. 2 provides atheoretical maximum in which only thermal or white noise is accountedfor. In practice, due to impulse noise, crosstalk, attenuation and delaydistortion, the maximum throughput that can actually be achieved will beless. Therefore, the data rates entered into the table should be reducedby a suitable amount to account for these additional factors.

Control program 31 then compares the calculated S/N ratio with theminimum required S/N ratio retrieved from database 33. If the calculatedS/N ratio exceeds the minimum required S/N ratio by more than a specificmargin, receiving modem 14 will send a message to transmitting modem 12requesting that the transmission power be decreased in step 40. As partof this message, receiving modem 14 could request a specific transmitpower value or, for simplicity, transmitting modem 12 could beinstructed to simply drop down to the next lower value in a table ofpossible transmit power levels stored in database 29. If the calculatedS/N ratio falls below the minimum required ratio by more than a specificmargin, receiving modem 14 will send a message to transmitting modem 12requesting that the transmission power be increased in step 42. Again,receiving modem 14 could request a specific transmit power value or,alternatively, transmitting modem 12 could simply move up to the nexthigher value in a table of possible transmit power levels. Iftransmitting modem is instructed to merely increment or decrement itstransmit power to the next available level, the process will repeatitself in iterative fashion beginning with step 36 until the calculatedS/N ratio falls within a predetermined range or margin about the minimumrequired ratio. This range or margin ensures that the two modems don'tendlessly chase one another in trying to close in on a satisfactorypower level to support a specific data rate. Alternatively, iftransmitting modem 12 is provided with an absolute transmit power valuefrom receiving modem 14, the process should complete after oneiteration.

It will be appreciated by those skilled in the art that more advancedand precise techniques can be used by other embodiments to calculate theminimum transmit power level that will support a given data rate. Forexample, transmitting modem 12 could transmit a test data pattern at astarting power level which would then be verified by receiving modem 14using any well known error detection technique. If the test pattern hasfewer than a certain minimum threshold of bit errors, receiving modem 14would instruct transmitting modem 12 to decrease the transmit power.Conversely, if the test pattern has more than the minimum threshold ofbit errors, transmitting modem 12 would be instructed to increase thetransmit power. Through successive iterations of this procedure, thetransmit power should end up at the level that just supports the datarate.

The example of FIG. 3 is directed towards an embodiment for adapting orminimizing the transmission power level for a fixed data rate.Conversely, there will be circumstances, as discussed hereinbefore,where it is desirable for other embodiments to fix the transmissionpower level and then adapt or maximize the data rate for that powerlevel. FIG. 4 provides a flow chart for data rate adaptation.

Referring now to FIGS. 2 and 4, the process begins with step 44 in whicha minimum transmission power is negotiated between transmitting modem 12and receiving modem 14. This negotiation can be carried out using thesame approach discussed earlier with respect to data rate negotiation.That is, one or both of modems 12 and 14 could maintain tables inmemories 26 and/or 30 that contain valid transmission power levels. Oneof the two modems 12 and 14 will propose a transmission power level tothe other modem during an initialization procedure, and, using anydesired protocol, the modems will exchange messages to arrive at anagreed upon minimum transmission power level.

Now that the minimum transmission power level has been established,receiving modem 14 will determine the net S/N ratio in step 46 in thesame manner as discussed earlier with respect to step 36 of FIG. 3.During step 46, control program 27 in transmitting modem 12 will choosea default data rate, which is stored in database 29, for use as astarting point in the adaptation process. This initial data rate willthen be transmitted to receiving modem 14 in a message.

In step 48, receiving modem 14 determines whether the calculated S/Nratio will support the initial data rate set by transmitting modem 12.Receiving modem 14 follows a similar procedure as that described earlierwith respect to step 38 of FIG. 3. First, control program 31 uses thecalculated S/N ratio to index the table stored in database 33 in whichminimum S/N ratios are correlated with a list of possible datatransmission rates and retrieves a maximum data rate. As part of theindexing procedure, control program 31 compares the calculated S/N ratiowith the minimum required S/N ratio entries stored in database 33. Whenthe calculated S/N ratio falls within a certain range or margin about aparticular S/N ratio entry, the data rate associated with that entrywill be retrieved. The margin or range value will be chosen based on thegranularity of entries in the database to allow control program 31 toconverge upon a choice. The margin or range is necessary because thecalculated S/N ratio will rarely correspond exactly to a table entry.

Next, if the data rate retrieved from the table is greater than theinitial data rate set by transmitting modem 12, receiving modem 14 couldrequest in step 50 that transmitting modem 12 increase the data rate tothe retrieved value or, alternatively, transmitting modem 12 could beinstructed to simply increment the data rate to the next higher value ina table of possible data rates stored in database 29. On the other hand,if the data rate retrieved from the table is less than the initial datarate set by transmitting modem 12, receiving modem 14 could request instep 52 that transmitting modem 12 decrease the data rate to theretrieved value or, alternatively, transmitting modem 12 could beinstructed to simply decrement the data rate to the next lower value ina table of possible data rates stored in database 29.

Similar to the case of transmit power adaptation, if transmitting modem12 is instructed to merely increment or decrement the data rate to thenext available level, the data rate adaptation process will repeatitself in iterative fashion beginning with step 48 until the transmitteddata rate converges upon the rate retrieved from the table in database33. Alternatively, if transmitting modem 12 is provided with an absolutedata rate value from receiving modem 14, the process should completeafter one iteration.

While various embodiments practice both the transmit power adaptationmethod of FIG. 3 and the data rate adaptation method of FIG. 4 usingin-band messaging between the two modems (i.e., using xDSL data channel54), in the preferred embodiment, embedded operational channel 56 (EOC)will be used. EOC 56 provides a low speed secondary channel on xDSL 16that allows the aforementioned methods to be practiced simultaneouslywith ongoing data transmission. Instead of sending test data tocalculate a S/N ratio at receiving modem 14, a S/N ratio can becalculated from a data transmission from an actual communicationsession.

Also, a typical application of the various embodiments will involve oneof the two modems 12 and 14 being located at a central office (CO) orremote terminal (RT) site with the other modem being located at acustomer site. This configuration allows the modem located at the CO,which, in FIG. 2, is transmitting modem 12, to be managed by networkmanagement system 58, external to the transmitting modem 12 asillustrated in FIG. 2. Through network management system 58, the tablesthat comprise databases 29 and 33 can be downloaded throughcommunication port 24 and periodically updated according to the currentxDSL application. The modem located at the customer site, which isreceiving modem 14 in the present example, can download the tables itneeds for database 33 from transmitting modem 12. Moreover, a techniciancan enter a particular performance parameter to be optimized (e.g.,transmission power level or data throughput) and fix values forparameters that will not be optimized through network management system58. Network management system 58 effectively eliminates negotiationsteps 34 and 44 of FIGS. 3 and 4 respectively, in which the modemsthemselves select which performance parameters will receive fixed valuesand which performance parameter will be optimized. Accordingly, in oneembodiment, the network management system 58 performs the selecting andfixing steps.

It will be appreciated by those skilled in the art that thefunctionality provided through control programs 27, 31 and databases 29,33 can also be implemented through hardware (e.g., an applicationspecific integrated circuit (ASIC) and supporting circuitry). Eachimplementation has its advantages, however. For example, hardware enjoysa speed and, arguably, a reliability advantage over software becausehardware testing and verification methods are currently more advancedthan software verification methods. On the other hand, software can beless expensive than customized hardware and offers greater flexibilityin adding or modifying product features.

Further, other embodiments comprising control programs 27, 31 anddatabases 29, 33 can be embodied in any computer-readable medium for useby or in connection with a computer-related system (e.g., an embeddedsystem such as a modem) or method. In this context of this document, acomputer-readable medium is an electronic, magnetic, optical,semiconductor, or other physical device or means that can contain orstore a computer program or data for use by or in connection with acomputer-related system or method. Also, the computer program or datamay be transferred to another computer-readable medium by any suitableprocess such as by scanning the computer-readable medium. Thus, thecomputer-readable medium could be paper or other suitable medium uponwhich the computer program can be printed, scanned with an opticalscanner, and transferred into the computer's memory or storage.

Thus far, the principles of the present invention have been applied to asingle pair of modems communicating in isolation. The advantages of thepresent invention, however, are perhaps most impressive when theseprinciples are applied to a modem pool environment.

As discussed earlier, crosstalk is one of the primary sources of noisein a communication system. Moreover, crosstalk is particularlydebilitating in a modem pool environment where many xDSL loops and othercircuits are bundled together in the same cable binder, which isstandard practice in a CO. While increasing signal transmission powercan improve the S/N ratio in a communication system, it unfortunatelycomes with the negative side effect of enhancing crosstalk with aneighboring system.

Other embodiments optimize the performance of an entire modem poolsystem by reducing crosstalk stemming from unnecessary transmit powerlevels. Referring now to FIG. 5, a communication system is shown inwhich a first pair 10 a of modems 12 a and 14 a communicating over xDSL16 a and a second pair 10 b of modems 12 b and 14 b communicating overxDSL 16 b suffer from crosstalk. The crosstalk results from xDSLs 16 aand 16 b being bundled together at one end in the same cable binder.Now, suppose transmitting modem 12 a of first pair 10 a is operating ata transmit power level that is greater than the minimum needed tosupport the current data rate. First pair 10 a can then achieve a lowertransmission power level using the process of FIG. 3 as describedherein. The reduction in transmission power by first pair 10 a has theeffect of reducing the level of crosstalk noise that bleeds into secondpair 10 b. Therefore, second pair 10 b can likewise negotiate a lowertransmission power level because of the reduction in crosstalk even ifsecond pair 10 b was currently operating at an optimum performance level(i.e., the transmission power is marginally sufficient to support thecurrent data rate). In theory, this process could go on in perpetuitywith both pairs alternately negotiating transmit power level reductions;however, this would be possible only in a system where crosstalk is theonly noise component. In all practical systems, there will always benon-crosstalk noise that will place a lower limit on transmission powerlevels. Nevertheless, in systems in which crosstalk is the dominatingnoise factor, the power savings can be dramatic.

In the example just described, second pair 10 b, which was initiallyoperating at a marginal performance level, reduced its transmissionpower while maintaining its current data rate or throughput in responseto the transmission power reduction by first pair 10 a. Alternatively,second pair 10 b could opt instead to increase its data rate using theprocess of FIG. 4 as previously discussed. In that circumstance, theentire system will enjoy an overall performance improvement comprisingboth a reduction in power consumption and an increase in throughput. Itshould be noted that in a multiple xDSL system, such as a modem pool, atleast one of the individual communication links (e.g., pairs in thepreceding example) must be operating above its marginal performancelevel. That is, it must be using a transmission power level greater thanthe level necessary to support its current data rate. For systemscomprising many communication pairs, a thorough performance improvementanalysis would be highly complex and thus require a computer simulation.Nevertheless, it should be clear to the skilled practitioner that theperformance of a large xDSL modem pool system can be tuned to attain adesired performance improvement through selective application oftransmission power and data rate adaptation. Advantageously, networkmanagement system 58 can be used extensively by a technician to targetthose communication links that will benefit the most from power and/ordata rate adaptation.

Note that through selective application of the xDSL performancecustomization principles discussed herein, the performance variancebetween xDSL communication pairs can be reduced. For example, recall theforegoing discussion with reference to FIG. 5 in which the second modempair 10 b had the option of undertaking a transmission power reductionor increasing its data rate in response to a transmit power reduction bythe first modem pair 10 a. Thus, assuming the first modem pair 10 a wastransmitting at a higher data rate than the second modem pair 10 b, thethroughput performance variance between the two pairs can be reduced byincreasing the data rate of modem pair 10 b.

The embodiments have been discussed as applied generally to an xDSLcomprising a data channel 54 and an EOC 56 (see FIG. 2). The principlesdisclosed, however, can be extended in other embodiments to the lowerlevel modulation techniques used in xDSL signaling. For example, ratherthan merely adapting transmission power uniformly across the entirety ofthe transmission spectrum, a frequency dependent embodiment can beimplemented in which the same principles are applied to selectedsub-bands within the spectrum. The concepts remain the same, except thereceiver will now measure the net S/N ratio in each sub-bandindividually and negotiate the transmission power level and/or data ratewithin only that band of the xDSL data channel. This approach would bepreferred for those xDSL systems using Discrete Multi-Tone (DMT)modulation in which the available bandwidth is divided into a set ofindependent, orthogonal sub-channels and then data is assigned to eachsub-channel according to the channel quality. Similarly, embodiments canbe applied to baseband systems by combining transmission poweradaptation with precoding and adaptive pre-emphasis in which some partsof the signal are attenuated and other amplified according to frequency.

In the examples presented, two variables, transmission power level anddata rate, were used as the optimization criteria. The embodiments arenot limited to the optimization of these two variables, however. Looplength is another variable that can be optimized. It is well known thatchannel attenuation increases as a loop length increases. Thus, longerloop lengths will require a corresponding increase in transmission powerlevel if the same data rate is to be maintained. The embodiments providethe skilled practitioner with the flexibility of weighing suchperformance factors as power consumption, throughput and loop length inan xDSL communication against one another to develop a customized systemhaving a performance profile tailored to the needs of a particularcustomer base. As customer needs change, the performance of the systemcan easily be altered to accommodate any new requirements.

In concluding the detailed description, it should be noted that it willbe obvious to those skilled in the art that many variations andmodifications can be made to the preferred embodiment withoutsubstantially departing from the principles of the present invention.All such variations and modifications are intended to be included hereinwithin the scope of the claims, as set forth in the following claims.

1. A method of adjusting transmit performance parameters over a digitalsubscriber line (DSL), the method performed in a first DSL modem, themethod comprising the steps of: negotiating, with a second DSL modem, alimiting value of a first performance parameter; receiving, from thesecond DSL modem, a signal exhibiting the first performance parameter,the received signal comprising a plurality of sub-bands, each sub-bandtransmitted at a respective transmit power level; determining asignal-to-noise-ratio for a sub-band of the received signal; andrequesting, from the second DSL modem, an adjustment in a secondperformance parameter associated with the sub-band of the receivedsignal, wherein the second performance parameter is different from thefirst performance parameter.
 2. The method of claim 1, furthercomprising the step of: receiving, from the second DSL modem, a secondsignal exhibiting the first performance parameter and the adjustment inthe second performance parameter.
 3. The method of claim 1, wherein thesecond performance parameter is transmit power level.
 4. The method ofclaim 1, wherein the second performance parameter is transmit data rate.5. The method of claim 1, wherein said negotiating step is performedafter the receiving step and before the determining step.
 6. The methodof claim 5, wherein said second performance parameter is transmit datarate and said first performance parameter is transmit power level. 7.The method of claim 5, wherein said second performance parameter istransmit power level and said first performance parameter is transmitdata rate.
 8. The method of claim 1, further comprising the step of:selecting the second performance parameter from a plurality of possibleperformance parameters.
 9. The method of claim 1, further comprising thestep of: repeating the receiving, determining and requesting steps untilthe first performance parameter of the received signal is marginallysupported.
 10. The method of claim 1, further comprising the step of:repeating, using the negotiated value for the first performanceparameter, the receiving, determining and requesting steps until thereceived signal marginally supports the adjustment to the secondperformance parameter.
 11. The method of claim 1, wherein receiving thesignal is over a primary channel and requesting the adjustment is over asecondary channel.
 12. The method of claim 1, wherein the limiting valueof the first performance parameter is a minimum value.
 13. The method ofclaim 2, further comprising the step of: receiving, from the second DSLmodem, a second signal exhibiting the first performance parameter andthe adjustment in the second performance parameter associated with thesub-band of the received signal.
 14. A receiving digital subscriber line(DSL) modem comprising: means for receiving, from a transmitting DSLmodem, a signal exhibiting a first performance parameter; means fornegotiating, with the transmitting DSL modem, a value for the firstperformance parameter; means for determining a signal-to-noise-ratio forthe received signal; and means for requesting, from the transmitting DSLmodem, an adjustment in a second performance parameter associated withthe received signal based at least in part upon thesignal-to-noise-ratio, wherein the second performance parameter istransmit data rate, and wherein the second performance parameter isdifferent from the first performance parameter.
 15. The receiving DSLmodem of claim 14, wherein said first performance parameter is transmitpower level.
 16. The receiving DSL modem of claim 14, furthercomprising: means for selecting the second performance parameter from aplurality of possible performance parameters.
 17. The receiving DSLmodem of claim 14, wherein: the received signal comprises a plurality ofsub-bands, each sub-band transmitted at a transmit power level; and themeans for determining the signal-to-noise-ratio for the received signalcomprises means for determining a signal-to-noise-ratio for a sub-bandin the received signal.
 18. The receiving DSL modem of claim 17, wherein the means for requesting comprises means for requesting an adjustmentin the second performance parameter associated with the sub-band of thereceived signal.
 19. The receiving DSL modem of claim 18, furthercomprising: means for receiving, from the transmitting DSL modem, asecond signal exhibiting the first performance parameter and theadjustment in the second performance parameter associated with thesub-band of the received signal.
 20. The receiving DSL modem of claim14, wherein the value for the first performance parameter is a limitingvalue.
 21. The receiving DSL modem of claim 20, wherein the limitingvalue for the first performance parameter is a maximum value.
 22. Thereceiving DSL modem of claim 14, wherein the signal is received over aprimary channel and the adjustment is requested over a secondarychannel.
 23. A system for adjusting transmit performance parameters overa digital subscriber line (DSL) comprising: means for negotiating, witha DSL modem, a maximum value for a first performance parameter; meansfor receiving, from the DSL modem, a signal exhibiting the firstperformance parameter, the signal comprising a plurality of sub-bands,each sub-band transmitted at a respective transmit power level; meansfor determining a signal-to-noise-ratio for the received signal; andmeans for requesting, from the DSL modem, an adjustment in a secondperformance parameter associated with the received signal based at leastin part upon the signal-to-noise-ratio, wherein the second performanceparameter is different from the first performance parameter.
 24. Thesystem of claim 23, wherein the means for determining comprises meansfor determining a signal-to-noise-ratio for a sub-band of the receivedsignal.
 25. The system of claim 24, wherein the means for requestingcomprises means for requesting an adjustment in the second performanceparameter associated with the sub-band of the received signal.
 26. Thesystem of claim 25, further comprising: means for receiving, from theDSL modem, a second signal exhibiting the first performance parameterand the adjustment in the second performance parameter associated withthe sub-band of the received signal.
 27. The system of claim 23, whereinthe signal is received over a primary channel and the adjustment isrequested over a secondary channel.
 28. A method of adjusting transmitperformance parameters over a digital subscriber line (DSL), the methodperformed in a first DSL modem, the method comprising the steps of:negotiating, with a second DSL modem, a maximum value for a firstperformance parameter; receiving, from the second DSL modem, a signalexhibiting the first performance parameter, wherein the received signalcomprises a plurality of sub-bands, each sub-band transmitted at arespective transmit power level; determining a signal-to-noise-ratio forthe received signal; and requesting, from the second DSL modem, anadjustment in a second performance parameter associated with thereceived signal based at least in part upon the signal-to-noise-ratio,wherein the second performance parameter is different from the firstperformance parameter.
 29. The method of claim 28, wherein thedetermining step comprises determining a signal-to-noise-ratio for asub-band of the received signal.
 30. The method of claim 29, wherein therequesting step comprises requesting an adjustment in the secondperformance parameter associated with the sub-band of the receivedsignal.
 31. The method of claim 28, further comprising the step of:repeating the receiving, determining and requesting steps until thefirst performance parameter of the received signal is marginallysupported.
 32. The method of claim 28, further comprising the step of:repeating, using the negotiated value for the first performanceparameter, the receiving, determining and requesting steps until thereceived signal marginally supports the adjustment to the secondperformance parameter.
 33. The method of claim 28, wherein the secondperformance parameter is transmit data rate.
 34. The method of claim 28,wherein the second performance parameter is transmit power level. 35.The method of claim 28, wherein said negotiating step is performed afterthe receiving step and before the determining step.
 36. The method ofclaim 35, wherein said second performance parameter is transmit datarate and said first performance parameter is transmit power level. 37.The method of claim 35, wherein said second performance parameter istransmit power level and said first performance parameter is transmitdata rate.
 38. The method of claim 28, further comprising the step of:selecting the second performance parameter from a plurality of possibleperformance parameters.
 39. The method of claim 28, wherein the signalis received over a primary channel and the adjustment is requested overa secondary channel.
 40. A receiving digital subscriber line (DSL) modemcomprising: a demodulator in communication with a transmitting DSLmodem; a memory; a central processing unit (CPU) in communication withthe demodulator and the memory; and a control program stored in thememory, the control program configured to, when executed by the CPU:negotiate, with the transmitting DSL modem, a limiting value of a firstperformance parameter; determine a signal-to-noise-ratio for a signalreceived from the transmitting DSL modem, the signal exhibiting thefirst performance parameter; and request, from the transmitting DSLmodem, an adjustment in a second performance parameter associated withthe received signal based at least in part upon thesignal-to-noise-ratio, wherein the second performance parameter istransmit data rate, wherein the second performance parameter isdifferent from the first performance parameter.
 41. The receiving DSLmodem of claim 40, wherein the control program is further configured toselect the second performance parameter from a plurality of possibleperformance parameters.
 42. The receiving DSL modem of claim 40, whereinthe control program is further configured to determine asignal-to-noise-ratio for a sub-band in the received signal, wherein thesub-band is transmitted at an associated transmit power level.
 43. Thereceiving DSL modem of claim 42, wherein the control program is furtherconfigured to request, from the transmitting DSL modem, an adjustment inthe second performance parameter associated with the sub-band of thereceived signal.
 44. The receiving DSL modem of claim 40, wherein thecontrol program is further configured to: receive, from the transmittingDSL modem, a second signal exhibiting the first performance parameterand the adjustment in the second performance parameter.
 45. Thereceiving DSL modem of claim 40, wherein said first performanceparameter is transmit power level.
 46. The receiving DSL modem of claim40, wherein the control program is further configured to repeatdetermining a signal-to-noise-ratio and requesting an adjustment untilthe first performance parameter of the received signal is marginallysupported.
 47. The receiving DSL modem of claim 40, wherein the controlprogram is further configured to repeat, using the negotiated limitingvalue for the first performance parameter, determining asignal-to-noise-ratio and requesting an adjustment until the receivedsignal marginally supports the adjustment to the second performanceparameter.
 48. The receiving DSL modem of claim 40, wherein the signalis received over a primary channel and the adjustment is requested overa secondary channel.
 49. A method of adjusting transmit performanceparameters over a digital subscriber line (DSL), the method performed ina first DSL modem, the method comprising the steps of: negotiating, witha second DSL modem, a value for a first performance parameter;receiving, from the second DSL modem, a signal exhibiting the firstperformance parameter; determining a signal-to-noise-ratio for thereceived signal; and requesting, from the second DSL modem, anadjustment in a second performance parameter associated with thereceived signal based at least in part upon the signal-to-noise-ratio,wherein the second performance parameter is transmit data rate, andwherein the second performance parameter is different from the firstperformance parameter.
 50. The method of claim 49, further comprisingthe step of: receiving, from the second DSL modem, a second signalexhibiting the first performance parameter and the adjustment in thesecond performance parameter.
 51. The method of claim 49, wherein saidnegotiating step is performed after the receiving step and before thedetermining step.
 52. The method of claim 51, wherein said firstperformance parameter is transmit power level.
 53. The method of claim49, further comprising the step of: repeating the receiving, determiningand requesting steps until the first performance parameter of thereceived signal is marginally supported.
 54. The method of claim 49,further comprising the step of: repeating, using the negotiated valuefor the first performance parameter, the receiving, determining andrequesting steps until the received signal marginally supports theadjustment to the second performance parameter.
 55. The method of claim49, wherein the received signal comprises a plurality of sub-bands, eachsub-band transmitted at a transmit power level.
 56. The method of claim55, wherein the determining step comprises determining asignal-to-noise-ratio for a sub-band of the received signal.
 57. Themethod of claim 56, wherein the requesting step comprises requesting anadjustment in the second performance parameter associated with thesub-band of the received signal.
 58. The method of claim 49, whereinreceiving the signal is over a primary channel and requesting theadjustment is over a secondary channel.